This is a Leopard issue. As a computer Tech I have done all the re-installs, software updates, firmware patches, dust cleaning , etc mentioned in the forums to try to fix this issue. My Mac Pro a year old dual 266 X2 with an ATI X1900 worked flawlessly until I ungraded/moved to Leopard. The only fix so far is the Vista shuffle back to Tiger, where the system again runs flawlessly, no matter what I throw at it, gaming, Aperture, you name it.

Never had a single problem with my x1900 in any Mac OS or Windows (and in games like UT3, UT2k4, etc).

I'm glad the blogosphere has finally reported on this issue. I have an early 2008 Mac Pro with the ati 2600 card. It froze right out of the box after the updates were installed. Anyways I just wanted to mention the absurd work around to this horrible bug... hook up a second monitor. No joke, I had crashes every hour or so, once I hooked up the second monitor the machine has been up for almost a week and a half now. People on the apple discussion forums are having sucess with this workaround for now.

I had this happen with my X1900 for a while. It was a first generation card. I called up Apple, explained what was going on and requested a 2nd generation card. They sent it, and all problems are gone now.

At least some of the first generation X1900 cards DO have a hardware problem leading to overheating. This is well documented, no reason to "theorize" at all. Shouldn't you fact-check what you post as news and try to get it accurate? If you are running Windows in Boot Camp, you can install the ATI drivers (from ATI instead of from Apple) and use the utility to watch the temperature of the card and see at exactly what temperature the problem occurs for you. There is a "version 2" revised card specifically to rectify this issue. A card which does this will gradually deteriorate over time and should be replaced!

This one appears to only be happening to users with a single monitor. Add a second monitor of any kind and problem appears to go away. Others have upgraded to the Nvida card and resolved the problem.

Speculation is the some of the ATI cards are overheating or the fan has stopped working. Some say the recent Mac Pro's with the ATI aren't having the problem. I have a recent Mac Pro and have not had the problem and running the box 10+ hours a day. Read the long thread on Apple discussion forum, some have resolve and others haven't.

I have a standard 8 core 2.8GHZ MacPro (Jan) with the bog standard ATI card. I have had zero freezes. I bought my MacPro 2 days after they came out. No heat issues either but then there is only one card.

I tried this fix by adding a second monitor to the system. Uptime now 1 day, 3 hours and 23 minutes without a glitch, no screen garbage, nothing amiss. I've tried to crash the system by duplicating things that brought the system to its knees every time before and everything runs perfectly.

Weird!